This invention relates to gate-source structures for static induction transistors and, in particular, to an etched source structure requireing relatively simple fabrication techniques.
The static induction transistor is a field effect semiconductor device capable of operation at relatively high frequency and power. The transistors are characterized by a short, high resistivity semiconductor channel which may be controllably depleted of carriers. The current-voltage characteristics of the static induction transistor are generally similar to those of a vacuum tube triode. The devices are described by Nishizawa et al in U.S. Pat. No. 3,828,230 issued Aug. 6, 1974.
The static induction transistor generally uses vertical geometry with source and drain electrodes placed on opposite sides of a thin, high resistivity layer of one conductivity type. Gate regions of opposite conductivity type are positioned on opposite sides of the source. During operation a reverse bias is applied between the gate region and the high resistivity layer causing a depletion region to extend into the channel below the source. As the magnitude of the reverse bias is varied, the source-drain current and voltage derived from an attached energy source will also vary.
The design and fabrication of the gate-source structure is difficult. In order to operate at frequencies near or above 1 GHz, the structures must be built under extremely precise dimensional control. Involved dimensions are in the micrometer range, requiring photolithographic alignments with submicrometer precision.
Gate-source structures having a surface-gate geometry generally have relatively low voltage gain and relatively good high frequency performance capability. On the other hand, gate-source structures having a recessed or buried-gate geometry generally have relatively high voltage gain and relatively poor high frequency performance capability. The poor voltage gain of surface-gate structures may be attributed to the particular shape of the active channel, which is wider in the region near the drain than in the region near the source.